Polymerization of ethylene in the prescence of ticl2 which has been activated by grinding



United States Patent PGLYMERIZATION 0F ETHYLENE IN THE PRES- ENCE 0F TiCl WHICH HAS BEEN ACTIVATED BY GRINDING Donald .F. Hoeg, Mount Prospect, Ill., and Frank X. Werber, Rockville, and Walter R. Wszolek, Ellicott City, Md, assiguors to W. R. Grace & Co., New York, N.Y., a corporation of Connecticut No Drawing. Filed Mar. 5, 1962, Ser. No. 177,248

12 Claims. (Cl. 260-88.2)

This invention is directed to polymerizing ethylene and mixtures of ethylene with propylene, butene-l, and transbutene-Z in the substantial absence of contaminants or inhibitors such as moisture, oxygen, acetylene, acetone, hydrogen sulfide, and the like, under moderate pressures in the presence of a catalyst made by grinding titanium dichloride in an inert medium similarly free of contaminants. It is essential that the grinding be continued until the surface area of the ground TiCl is in the range of about -1*O30 square meters per gram, as measured by, for example, the well-known mixed helium-nitrogen absorption technique, Nelson, F. M., and Eggertsen, F. T., Anal. Chem., 30, p. 1387 (1958).

The catalyst so prepared has been found to be much more active in olefin-polymerization than titanium dichloride that has not been so prepared. The reason for the increased activity is not fully known. It appears, however, that the freshly fractured surfaces of the ground particles are extremely active if not allowed to come in contact with moisture, oxygen, or certain other poisons, and that such surfaces may account for the increase in activity. It further appears that this increase cannot be accounted for by an increase in surface area.

The TiCl catalyst so prepared is useful in making high-molecular weight polymers from ethylene-rich feed streams. It is operable at temperatures ranging from room temperature up to 300 C. and higher, and at pressures from a few atmospheres, e.g., 100 p.s.i.g., to 5000 p.s.i.g., and even higher. For practical operation, however, temperatures 'in the range of 50-270 C. and pressures of 200 to 600 p.s.i. are suitable.

The polymerization reaction is operable with or without a solvent. If a solvent is used, it should be one which is liquid under the conditions of temperature and pressure used, and which contains no contaminants as aforesaid. Hydrocarbon solvents are preferred, e.g., pentane, hexane, heptane, cyclohexane, octane, benzene, xylene, toluene, and the like.

The amount of catalyst is not critical. Relatively small amounts are operable to form relatively large amounts of polymer. In general, a practical range is 0.001 to 1 g. of catalyst per gram of olefin polymerized. Even larger amounts are operable, but unnecessary.

The following examples illustrate the invention, but do not limit it.

EXAMPLE l.GRINDING TiCl CATALYST the rolls from time to time and opened in a dry box maintained under a slight pressure of argon, and the product was sampled. Aliquots of each such sample were analyzed for TiCl TiCl and free Ti; the surface area was determined; and the sample was used in a polymerization run and its activity determined.

The material before milling was black and had a granular crystalline appearance. After milling it was still black, but had a soft amorphous appearance. In general, after milling, it is extremely pyrophoric.

It is essential that the TiCl be ground in the substantial absence of oxygen, moisture, and similar contaminants, e.g., CO, acetylene, NH and ethers, ketones, and other oxygen-containing organic materials. (Olefins and saturated hydrocarbons, however, are not contaminants.) In addition to argon, we have found that lamp-grade nitrogen, e.g., nitrogen .of a purity suitable for filling light bulbs, is suitable. Also suitable are the other noble gases (pure), especially helium, and neon. The same precautions against contaminants applicable in milling also apply to handling, storing, and using the milling material.

Throughout this specification it will be understood that all samples of activated TiCl are weighed and added to the autoclave under inert conditions equivalent to the conditions of activation as regards freedom from contaminants.

EXAMPLE 2.-SYNTHESIS OF POLYETHYLENE WITH GROUND TiCl Using the aforesaid precautions, 1.46 g. TiCl ball-milled five days under argon to give a surface area of about 27 square meters per gram was placed in a 1-liter stainless steel autoclave equipped with stirrer, thermowell, rupture disc, a ball valve serving as catalyst inlet, and an inlet for charging solvent and gases. Next, 300 cc. of pure, dry cyclohexane (solvent) was added. The stirrer was then turned on, and the autoclave was heated to about C. Then the autoclave was connected to the ethylene tank, pressured to 470 p.s.i.g., and maintained under this ethylene pressure throughout the run. The ethylene used was likewise very dry and quite pure.

The run proceeds (typically) at a temperature ranging between about 150 and about C. Considerable variation in temperature is, however, possible in using activated TiCl After 17 minutes the run was stopped and the autoclave was cooled (to below the boiling point of the solvent), and was then vented and opened. The polyethylene-containing reaction slurry in cyclohexane was then transferred to a liter beaker. At this stage the product was black, owing to the TiCl content.

If desired, the crude material may be purified and recovered by techniques well known in the art. For example, the material may be refluxed with alcoholic acids, e.g., HCl-met-hanol, followed by filtration and drying.

The product purified as above was found to weigh 50.5 g., with a density of 0.9490.

Using the well known formula for determining catalyst activity (grams of polymer/grams of catalyst/per hour) it will be seen that this particular catalyst has an activity of 50.6-:1.46 =122.0.

In a comparable run, using TiCl that had not been ball-milled, and having a screen analysis such that over 60% passed a 60 mesh screen, 1.18 g. of such catalyst was used for 1 hour with a yield of 3 g. of polyethylene. The

catalyst activity was therefore Since the yield was smaller and the amount of catalyst and the reaction time greater, it is clear that ball-milling gives a much more active catalyst. In another control run (at a lower temperature) 1.86 g. of finely divided TiCl of commerce, not ground under inert conditions, was used as the catalyst to polymerize ethylene in cyclohexane at 120-130" C. under 450 p.s.ig. for 3% hours. The meld Patented Apr. 12, 1966 7 3 of polyethylene was 5 g. The catalyst activity was therefore V Further runs carried out using the activated TiCl of this invention and substantially the same techniques of Example 2 above are summarized in Table I, below. The solvent in each case was toluene (1.66 lb.). The catalyst Was TiCl ball-milled 119 hours under argon, and it had a surface area of substantially 27 square meters per gram.

Table l Polyethylene Example Catalyst, g. Temp., Press, Time, Catalyst N C. p.s.i. ruins. aetivlty G. Density EXAMPLE 6.-ETHYLENE/PROPYLENE COPOLYMERIZATION As already mentioned, the milled TiCl catalyst is also elfective with ethylene-propylene mixtures. E.g., using the general procedure of Example 2, 1.32 g. of the same TiCl (ball-milled five days under argon), 300 ml. purified cyclohexane, and 22 m1. liquid propylene was placed in the autoclave, which was then sealed and heated to 145 C. When it reached this temperature it was pressured with ethylene to 450 p.s.i. The polymerization wasrun at 140 C. for 32 minutes, after which the autoclave was vented, cooled, and the polymer recovered. The purified polymer had a density of about 0.93 and a propylene content of about 6% (by infra-red measurement). On pressing -it gave a rubbery film.

EXAMPLE 7.ETHYLENE/PROPYLENE COPOLYMERIZATION EXAMPLE 8.-ETHYLENE/BUTENE-1 COPOLYMER The run was made in a 1-liter vertical stirred autoclave. The catalyst was 1.06 g. TiCl ball-milled five days in argon, and had a surface measurement of about 27 square meters per gram. The solvent was 0.66 lb. toluene. Twenty ml. butene-l was added, and the autoclave heated to 175 C. and pressured to about 425 p.s.i. with ethylene. It was repressured to this pressure from time to time during the ensuing one hour run. The product was worked up and found to weigh 61.7 g., density 0.9175, giving a catalyst activity of 112. Analysis showed that about 2.1 mole percent butene-l was incorporated into the copolymer.

EXAMPLE 9.-COPOLYM-ER OF ETHYLENE/ TRANS-BUTENE-2 of TiCl; ball-milled under argon five days, to give a ethylene in amounts up to about 20 mole percent of the total feed.

EFFECTS OF GRINDING TiClz There are certain curious changes in the T iCl mass on ball-milling.

Firstly, the surface area (square meters per gram) increases, rapidly at first, then more slowly, reaching a peak at about 1-5 days, more or less, depending somewhat on hardness of apparatus, load, milling rate, etc. Ordinarily, this area peak does not correspond with catalyst activity peak, which generally occurs well before the area peak. After the area peak is reached, further milling causes a gradual decline inarea. With this area decline, activity also declines, and may drop surprisingly after the 6th day of milling.

Accordingly, We consider it essential that the grinding be continued until the surface area reaches at least 10 square meters per gram. Under ordinary conditions this "condition is reached in about one day of ball-milling. Generally speaking, it can be reached sooner if the mill is run somewhat faster, or may 'be delayed if the mill is run somewhat more slowly. As the grinding progresses, the surface area reaches a maximum of about 25-30 square meters per gram, typically at about the 5th dayo f normal milling. Thereafter, continued milling causes the area to decrease. When it decreases below about 17 square meters per gram, its activity is markedly reduced. There;- fore, while the surface area range for which the catalyst is most effective extends from 10 to 30 square meters per gram, it must be understood that if the surface is 10-17 square meters per gram, this was reached in the initial phases of grinding, and not as a result of further grinding after the maximum surface (e.g., 25-30 metersfi/ gram) was reached and passed. For any given example having a surface area in the 10-17 square meters range, it may readily be determined whether it has or has not been ground through its maximum surface simply by analyzing for TiCl If it has not been ground through its maximum area, the TiCl will be at least about 45 weight percent. If it has been ground through its maximum, such TiCl (surface area 10-17 meters /g.) will have a TiCl content of about 35% or less. (This change in chemical composition will be discussed in more detail below.)

Another important change in the TiCl caused by grinding is the development of a new crystalline phase for the TiCl The X-raypowder pattern of the technical grade titanium dichloride (e.g., prepared by heating together TiCl and Ti metal) shows a diffraction spectrum almost identical to that described for pure TiCl We shall call the structure represented by this pattern Phase A. Upon milling technical grade TiCl for about one day, a new crystalline phase (Phase B) appears, whose diffraction pattern does not closely resemble any of the published patterns for either the dior trichloride. After five days milling, Phase A is completely gone and B is the only one visible. For good catalyst activity, a substantial proportion of the TiCl must be in the form of this new Phase B.

No evidence for crystalline, metallic titanium can be found. In fact, the metallic residue from the milled samples (after dissolution) of the halides, was shown to be amorphous by separate X-ray examination. Based on the above, we conclude that the milling process brings about a migration of titanium ions within the TiCl lattice. These aggregate to form amorphous titanium metal, leaving holes behind, Accordingly, the structure of Phase B is apparently caused by a slight shift in the inter-layer Ti to Ti distance, due to a change in stacking order of adjacent layers, brought about by the formation of holes in the original TiCl (Phase A) structure.

As has already been mentioned, grinding causes a change in the chemical composition of the TiCl viz., the TiCl slowly disproportionates to TiCl and Ti, according to the following equation:

3TiCl 2TiCl +Ti Referring to Table II, it will be evident that the decrease in TiCl and the increase in TiCl and Ti can be accounted for by the mechanism of the foregoing equation. The catalyst activities in the table were determined by using the catalyst to polymerize ethylene by the general procedure of Example 2.

(Incidentally, it may be here noted that the TiCl of commerce, being generally made from TiCl and Ti, may be expected to contain small amounts of these two materials.)

The reasons why grinding TiCl increases its activity as a polyethylene catalyst are not clearly understood. As shown in Table II, the surface area of the catalyst is increased by grinding, as may be expected. However, it is equally clear that activity is not a simple function of surface area. For example, the surface area of the catalyst of Example 13 is 27 square meters per gram, with an activity of 93.7, whereas the surface area of the catalyst of Example 11 is only 10.7, but with an activity of 1212. Also, in comparing the catalysts of Examples and 1, it is noted that increasing the surface area by a factor of 3-5 increases the activity by a factor of about 70. In considering the TiCl content of the g-round catalysts, it will be observed that activity is roughly correlated to the percentage of TiCl in the catalyst. On the other hand, the percent of TiCl in a ground catalyst is always less than that in an unground catalyst owing to the disproportionation reaction above discussed, and yet the unground catalyst is much less active than the ground catalyst.

TABLE II PHYSICAL AND CHEMICAL CHANGES OCCURRING WHILE BALL-MILLING TiClz The two following examples provide more complete working data for the catalysts of Examples 10 and 11.

EXAMPLE 10 (CONTROL) Following the procedure of Example 2, 0.71 gram of unground TiCl catalyst was placed in the autoclave with 0.66 pound of toluene. The polymerization temperature was 148-l66 C., the pressure was 475-540 p.s.i., the reaction time was one hour and three minutes, and the yield of solid polyethylene was 1.3 grams.

EXAMPLE 1 1 Following the procedure of the preceding example, 1.08 grams of the catalyst was used, the polymerization temperature being 154-1 68 (1., the pressure 420-450 p.s.i., the reaction time 30 minutes, and the yield 65.5 grams. The solvent was 0.66 pound toluene.

The uses of the polyolefins of this invention are analogous to those prepared by prior art procedures. The solid polymers can be used to make moldings, film, filament, pipe, tubing and the like, using substantially the same equipment and technique customary for the solid polyolefins of the prior art.

This application is a continuation-in-part of our copending application, Serial No. 831,719, filed August 5, 1959, now abandoned, which in turn is a continuation-in-part of our application, Serial No. 687,614, filed October 2, 1957, now abandoned.

We claim:

1. In the method of polymerizing feed which is a member of the group consisting of ethylene and mixtures of ethylene with a member of the group consisting of propylene and a butene with finely divided TiCl catalyst, in an inert diluent at superatmospheric pressure, the improvement comprising activating the TiCl before use by grinding it in an inert atmosphere until the surface area is 10-30 square meters per gram and discontinuing the grinding before the TiCl content of the catalyst drops below 35 weight percent.

2. The method according to claim 1 in which the grinding is continued until the surface area of the catalyst is 25-30 square meters per gram.

3. The method according to claim 1 in which the polymerization is carried out at a temperature in the range 50-270 C. and at a pressure of 200-600 psi.

4. The method according to claim 3 in which the feed is ethylene.

5. The method according to claim 3 in which the feed is a mixture of ethylene with a co-monomer which is a C -C olefin.

6. The method according to claim 5 in co-monomer is propylene.

7. The method according to claim 5 in co-monomer is a butene.

8. The method according to claim 7 in co-monomer is butene-l.

9. The method according to claim 7 in butene is trans-butene-Z.

10. The method according to claim 1 in diluent is a hydrocarbon.

11. The method according to claim 1 in which the TiCl before grinding consists essentially of 87.5% TiCl 6.8% TiCl and 1.4% Ti, and after grinding consists essentially of 39-76.7% TiCl 16.7-50.3% TiCl and 2.4-7.8% Ti.

12. The method according to claim 1 in which the T-iCl after grinding consists essentially of about 76.7% TiCl 16.7% TiCl and 2.4% Ti, and has a surface area of about 10.7 meters per gram.

References Cited by the Examiner UNITED STATES PATENTS 7/ 1959 Seelbach 26093.7 8/ 1959 Schreyer 26093.7

FOREIGN PATENTS 1,132,506 11/1956 France.

778,639 7/1957 Great Britain.

JOSEPH L. SCHOFER, Primary Examiner.

JAMES SEIDLECK, Examiner.

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1. IN THE METHOD OF POLYMERIZING FEED WHICH IS A MEMBER OF THE GROUP CONSISTING OF ETHYLENE AND MIXTURES OF ETHYLENE WITH A MEMBER OF THE GROUP CONSISTING OF PROPYLENE AND A BUTENE WITH FINELY DIVIDED TICL2 CATALYST, IN AN INERT DILUENT AT SUPERATMOSPHERIC PRESSURE, THE IMPROVEMENT COMPRISING ACTIVATING THE TICL2 BEFORE USE BY GRINDING IT IN AN INERT ATMOSPHERE UNTIL THE SURFACE AREA IS 10-30 SQUARE METERS PER GRAM AND DISCONTINUING THE GRINDING BEFORE THE TICL2 CONTENT OF THE CATALYST DROPS BELOW 35 WEIGHT PERCENT. 